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st: data management


From   "Sim.Oertel@t-online.de" <Sim.Oertel@t-online.de>
To   statalist@hsphsun2.harvard.edu
Subject   st: data management
Date   Mon, 26 Mar 2007 07:48:45 +0200

Dear Statalist members,

I have a question regarding the definition of a new variable in a data
set. I would like to define this new variable in the way that it will
tell me how many subjects with a specific characteristic exist at a
specific time. For example:  Suggesting a simplified data set of nine
subjects with information regarding their market-entry, market-exit, and
size. In this case, I would like to know how many subjects with the size
6 were in the market at the same time with each other subject. 

Example:
ID            Market-Entry             Market-Exit         Size         
 New_Variable
1             10                             98                       1 
               1
2             15                             80                       1 
               0
3             30                             110                     1  
              2
4             41                             97                       1 
               1
5             76                             85                       1 
               1
6             77                            218                      2  
              2
7             85                            220                      3  
              2
8             82                            118                      6  
              2
9             99                            218                      6  
              2


For ID1, for example, subject 8 entered at time 82, while ID1
markets-exist is 98. The other subject with size 6 is ID9. But ID9
entered the market after the market-exist of ID1. So the variable should
hold the value 1 (One subject with size 6 was present in the market at
the same time as ID1). Regarding subject ID2, ID8 and ID 9 entered after
the market-exit of ID2, so the new variable should hold the value 0. For
ID3, the new variable should hold the value 2, because both subjects
with the size 6 were present in the market at the same time than ID3,
and so on.

I really appreciate for any help and suggestions.

Simon








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